Biometric imaging device compensating for non-biometric parameters

ABSTRACT

Provided is a biometric imaging device for imaging a biological feature, which includes a sensor for detecting an environmental parameter other than relating to surface topology of the biological feature. The detected environmental parameters like temperature and humidity levels are utilized in image reconstruction to eliminate erroneous structures caused by the environmental conditions. There is also provided a biometric imaging device, which includes a preparation device for use prior to sensing a biometric image. The preparation device is used for conditioning a parameter of the biometric information source, and/or for cleaning the biometric information source.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of application Ser. No. 10/173,439,filed Jun. 18, 2002, entitled “BIOMETRIC IMAGING DEVICE COMPENSATING FORNON-BIOMETRIC PARAMETERS” which claims the benefit from ProvisionalApplication No. 60/305,187, filed Jul. 16, 2001.

FIELD OF THE INVENTION

This invention relates generally to biometric imaging devices and moreparticularly to biometric imaging devices for imaging biometric surfacescapable of compensating images according to non-biometric parameters.

BACKGROUND OF THE INVENTION

With the increasing importance of personal identification for thepurpose of security in remote transactions in today's world ofelectronic communication, biometric identification techniques arerapidly evolving into a pervasive method for personal verification.Among the different biometrics proposed for such a purpose, such asfingerprints, hand prints, voice prints, retinal images, handwritingsamples and the like, fingerprint analysis is amongst the best studiedbiometric techniques. Fingerprint sensing and matching is a reliable andthus widely used practice for personal identification or verification.In a common approach to fingerprint identification, a live fingerprintis scanned and electronically digitized. The digitized data generallycontains information pertaining to characteristic features of thefingerprint, such as ridge endings, points of ridge bifurcation, and thecore of a whorl, i.e. fingerprint minutiae. The digitized data is thencompared with stored data relating to fingerprints that have beenobtained previously from corresponding authorized persons, i.e.fingerprint templates. When a match is detected, within a predeterminedlevel of security in the form of a predetermined acceptance rate, theindividual is identified and a corresponding action is performed.

In general, there are two types of errors associated with fingerprintidentification. The first is a false reject or Type I error, and thesecond is a false accept or Type II error. A type II error occurs whenthere is sufficient similarity between fingerprints of two individualsthat one is mistaken for the other. A Type I error occurs for a varietyof reasons, and refers to when an individual is not identified eventhough the individual is an authorized user registered with the system.

It has been suggested that the underlying cause of errors in fingerprintanalysis is that the amount of data from a fingerprint is too limitedfor it to be used in a biometric identification system involving a largenumber of users. Increasing resolution of the imaging devices to capturemore detailed images of fingerprint minutiae, as well as theconsideration of pore patterns of biological surfaces have both beenapplied to reduce the error rates which occur in fingerprintidentification.

The above-mentioned causes for failures in fingerprint verification areclosely related to the applied imaging and analyzing techniques, and aretypically responsible for Type II errors. There are, however, othersources for identification errors, which are primarily of anon-biometric nature. As part of a human body, the finger and moreparticularly the skin is submitted to the same physiological basic rulesas any other part of the human body. The skin has elastic propertiesthat allow a certain degree of flexibility either in extending or in aconstricting fashion. For example, in cold temperature conditions, theblood circulation in the extremities like fingers is reduced to maintainthe body temperature. Conversely, in warmer temperature, the blood flowis increased. Thus, the condition of the fingertip and therefore thefingerprint profile itself may vary depending on the properties of theskin and the environmental conditions. This also implies slightmodifications of the fingerprint to be characterized. Furthermore, thehygienic conditions of a hand, and more particularly that of thefingertip to be imaged, are also factors for possible interference inproperly imaging a fingerprint. All this causes problems in areproducibility of a fingerprint imaging process, and in turn leads toan increase in Type I or false reject error rates.

It is highly advantageous to provide a biometric imaging device capableof compensating for non-biometric parameters, by either providingwell-defined conditions for imaging a biological surface, or by sensingand correcting for conditions prevalent during the process of imagingthe biological surface. It is of further advantage to reduce the Type Ierror rates in a given fingerprint identification process, thusenhancing the reliability of fingerprint imaging devices.

OBJECT OF THE INVENTION

It is therefore an object of the instant invention to provide abiometric imaging device incorporating a sensor for sensing externalparameters potentially interfering with biometric characteristics.

It is another object of the instant invention to provide a biometricimaging device allowing to compensating for non-biometric parametersinterfering with biometric characteristics.

It is further an object of the instant invention to provide a biometricimaging device comprising a preparation station for providingwell-defined and reproducible conditions of the skin to be scanned.

SUMMARY OF THE INVENTION

According to an aspect of the present invention, there is provided abiometric imaging device for imaging a biological feature, the biometricimaging device comprising a first sensor for sensing the biologicalfeature and for providing sensed image data relating to an image of asurface of the biological feature, a second sensor for detecting anenvironmental parameter other than relating to surface topology of saidbiological feature, and a processor for receiving the sensed image dataand the detected environmental parameter and for correcting or restoringthe sensed image data in dependence upon the detected environmentalparameter.

According to an aspect of the present invention, there is furtherprovided a method for imaging a biological feature comprising the stepsof sensing the biological feature and providing sensed image datarelating to an image of a surface of the biological feature, detectingan environmental parameter other than relating to surface topology ofsaid biological feature, and correcting or restoring the sensed imagedata in dependence upon the detected environmental parameter.

According to another aspect of the present invention, there is provideda biometric imaging device for imaging a biological feature of abiometric information source, the biometric imaging device comprising acapacitive contact imaging device that senses the biological feature andprovides sensed data relating to an image of the biological feature, anda preparation device contacting the biological surface temporarily nearand/or simultaneously with a sensing of the biological surface, thepreparation device adapted to condition a parameter of the biometricinformation source.

According to another aspect of the present invention, there is furtherprovided a method for imaging a biological feature of a biologicalinformation source comprising the steps of manipulating an environmentalparameter of the biological information source and sensing image data ofthe biological feature, after manipulating the environmental parameter.

According to yet another aspect of the present invention, there isprovided a method for imaging a biological feature of a biologicalinformation source comprising the steps of cleaning the biologicalinformation source; and sensing image data of the biological feature,after cleaning the biological information source.

According to yet another aspect of the present invention, there isfurther provided a biometric imaging device comprising a swipe contactimager disposed for having a fingertip passes there across, and acleaning station disposed adjacent the swipe contact imager for havingthe fingertip passed there across, portions of the fingertip contactingthe cleaning station prior to passing across the swipe contact imager,wherein in use portions of the fingertip are cleaned prior to beingimaged in order to provide for imaging of a clean fingertip.

BRIEF DESCRIPTION OF THE DRAWINGS

Exemplary embodiments of the instant invention will be described inconjunction with the following drawings, in which similar referencenumbers designate similar items:

FIG. 1 is a simplified block diagram of a prior art sensing deviceshowing a sensing pad comprising a linear capacitive sensing array;

FIG. 2 is a simplified block diagram of a biometric imaging deviceaccording to a first embodiment of the present invention;

FIG. 3 is a simplified block diagram of a biometric imaging deviceaccording to a second embodiment of the present invention;

FIG. 4 is a simplified block diagram of a biometric imaging deviceaccording to a third embodiment of the present invention;

FIG. 5 is a simplified block diagram of a biometric imaging deviceaccording to a fourth embodiment of the present invention;

FIG. 6 is an image of a fingertip sensed under dry conditions; and

FIG. 7 is an image of a fingertip sensed under moist conditions.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

The method and system of the present invention are now described withreference to a capacitive contact swipe imager for sensing a biologicalsurface. Of course, the present invention is not restricted to swipeimagers, or to capacitive contact imagers, but is optionally used withoptical imagers, thermal imagers, and other types of imaging devices.Further, the invention is not restricted to imaging a fingerprint or abiological surface, but generally applies to imaging any biologicalfeature that is susceptible to external conditions. An exemplarycapacitive contact imager driver circuit is described in detail in U.S.Pat. No. 5,778,089 to Borza issued Jul. 7, 1998, incorporated herein byreference. An exemplary capacitive contact swipe imager is described indetail in U.S. application Ser. No. 09/984,354, filed Oct. 30, 2001, andincorporated herein by reference.

In the capacitive contact swipe imager, a biometric information sourceis passed over a sensing pad, and data is recorded during the motion ofpassing over. The sensing pad comprises a plurality of individualcapacitive sense elements, which are typically arranged in arrays ofrows and columns. Preferably, in order to generate an image foranalysis, a capacitive sensing element is smaller than half the smallestfeature size to be sensed. Empirical studies have shown that a squareplate of about 50 μm edge length is suitable for fingerprint sensing.

The capacitive sensing elements are arranged as to form individuallinear capacitive sensing arrays within a same sensing pad. Within eachlinear sensing array the rows are equally spaced by a given row spacing,and the columns are equally spaced by a given column spacing. Eachlinear capacitive sensing array has a capacitive detective area and aresolution, depending on an area and a number of rows and columnsforming the linear capacitive sensing array. In practice there are about10 rows and 200 columns of regularly spaced elements, occupying an areaof approximately 0.1×2 cm², in a representative linear capacitivesensing array. The capacitive sensing element density of the linearcapacitive sensing array, which is inversely proportional to the rowspacing and the column spacing of the linear capacitive sensing array,determines the resolution of the linear capacitive sensing array.

Referring to FIG. 1, a simplified block diagram of the capacitivecontact swipe imager according to prior art is shown. A sensing pad 11comprises a linear capacitive sensing array 12. The sensing pad has anarea of approximately 3×2 cm² for accepting a fingertip drawn across thesensing pad. In this example, the linear capacitive sensing array 12comprises 10 rows and 300 columns. The linear capacitive sensing array12 is connected through an analog switch matrix to facilitate reading ofthe image of a biological surface. Timing and sequencing logic (notshown) selects each element in the array, in turn, to produce a completeimage of a fingerprint presented to the device.

During the swiping process, a series of partial snapshots of thefingerprint are recorded. The individual images have a sensing timedifference r , which is determined by the timing and sequencing logic. Areconstruction of a composite image representative of the biologicalsurface scanned is based on finding overlapping areas between capturedpartial images; the reconstruction is achieved for example in apuzzle-like fashion. A processor (not shown) is used to correlate datacorresponding to the individual partial images with each other and withpreviously stored sample data.

Referring to FIG. 2, a simplified diagram of a first embodiment of abiometric imaging device according to the instant invention is shown.The biometric imaging device is based on the above-described capacitivecontact swipe imager. Alternatively, the present invention is based onanother type of contact imager, another type of swipe imager, an opticalimager, a thermal imager, or the like.

The biometric imaging device 20 includes a sensing pad 21, whichcomprises a linear capacitive sensing array 22. The biometric imagingdevice 20 further includes a processor 23, as well as a sensor 24 forsensing external conditions. The parameters sensed by the sensor includeambient temperature and ambient humidity. Both the linear capacitivesensing array 22 as well as the sensor 24 are connected to the processor23. A biological surface, for example a fingertip, is passed over thesensing pad 21, and a plurality of partial images is captured by thelinear capacitive sensing array 22, and processed by the processor 23.The processor 23 constructs a composite image from the plurality ofpartial images. During image construction, the data sensed by the sensor24 are taken into account by the processor 23.

In order to perform a best possible analysis of the biological surface,the processor 23 automatically introduces those parameters sensed by thesensor 24 for taking into account the physiological conditions of thebiological surface imaged during the image process. For example, whenused in Canada during winter, the extreme environmental conditionsdecrease the elasticity of the skin and conversely increase the drynessof the skin. Therefore, when sensing for example, a fingerprint, theprocessor 23 transforms the image of the fingerprint accordingly, usingfor example a similarity transformation. This way, a processed image isobtained corresponding to predetermined or averaged environmentalconditions for which the physiological characteristics of the skin arewithin predetermined or averaged limits.

Referring to FIG. 3, a simplified diagram of a second embodiment of abiometric imaging device according to the instant invention is shown.The biometric imaging device 30 again includes a sensing pad 31, whichcomprises a linear capacitive sensing array 32, a processor 33, as wellas a sensor 34. The sensor 34 is for sensing the conditions of thebiological surface to be imaged. The biometric imaging device 30 furtherincludes a roller 35 for guiding a biological surface to be imaged, forexample a fingerprint, towards the linear capacitive sensing array 32.The sensor 34 is disposed between the sensing pad 31 and the roller 35.This way, it is most likely that the data sensed by the sensor 34corresponds to the condition of the biological surface sensed by thelinear capacitive sensing array 32. Both the linear capacitive sensingarrays 32 as well as the sensor 34 are connected to the processor. Whenin use, a biological surface to be imaged, such as a fingertip, ispositioned on the roller 35 and pushed forward towards the sensing pad31. While moving forward, the fingertip passes over the sensor 34, wherephysiological parameters such as dryness and/or temperature are read.The sensor 34, which is connected to the processor 33, communicates thephysiological information. In the example of using the biometric imagingdevice 30 in Canadian winter conditions, a temperature of the fingertipis lower than an average body temperature of 37° C., and a high degreeof dryness is measured for the skin of the fingertip. The processor 33receives the sensed information and includes the parameters foranalyzing the fingerprint image. The analysis of the image data takesinto account that because the skin is affected by the environmentalconditions, the pattern of the fingerprint features is thereby affected.Therefore, the processor 33 transforms the image of the fingerprintaccordingly to obtain a processed image corresponding to predeterminedor averaged environmental conditions. Of course, the compensationsinduced by the processor 33 are different in warmer conditions becausethey depend upon the reading of the sensor 34. Other parameters sensedby the sensor 34 are for example a humidity level of the biologicalsurfaced to be imaged. A high content of adherent moisture affects therelative height and depth of ridge and valley structures of fingerprintprofiles. Thus, it is the detail of the ridge and valley structures thatis lost in certain areas due to the collection of excessive moisture inthe valleys. Appropriate data processing algorithms used during imagereconstruction are possibly applied in order to restore undisturbeddetail information.

Referring to FIG. 4, a simplified diagram of a third embodiment of abiometric imaging device according to the instant invention is shown. Asdescribed above for the first and second embodiment, the biometricimaging device 40 includes a sensing pad 41, comprising a linearcapacitive sensing array 42, a processor 43 and a sensor 44. In thethird embodiment, a cleaning station 46 is added to the biometricimaging device 40. Optionally, a roller is also added to the biometricimaging device 40. The cleaning station allows for cleaning thefingertip prior to imaging the fingerprint. It thus allows for removingas much dust or any impurity as possible for improving the quality ofthe image. A cleaning process in the form of, for example, a hand lotiondispenser, an air jet dispenser, a wire brush, a series of sponges forwetting and drying the fingertip alternately in order to remove dirtknown to cause imaging problems, or any other convenient cleaningprocess is used. Advantageously, the cleaning station is disposed in aposition for cleaning the fingertip before the fingerprint is imaged.

Referring to FIG. 5, a simplified diagram of a fourth embodiment of abiometric imaging device according to the present invention is shown.The biometric imaging device 50 includes a sensing pad 51, comprising alinear capacitive sensing array 52, a processor 53 and a sensor 54. Thesensor detects the ambient temperature and the ambient moisture levelfor the biometric imaging device. Alternatively, the sensor 54 isinstalled in a way, so that the sensor 54 detects the physiologicalconditions of a biological surface to be imaged, such as a fingertip,the physiological conditions being for example the temperature and thedryness of the fingertip. Optionally, a roller is added to the biometricimaging device 50. Further optionally, a cleaning station is added tothe biometric imaging device 50. The sensor 54 as well as the linearcapacitive sensing array 52 are connected to the processor 53. Further,two compensating devices 57 and 58 are added to the biometric imagingdevice. The compensating devices are possibly provided in the form of amoisturizer 57 for compensating for dryness and of thermal unit 58 forapplying heat. Alternatively, only one or more than two compensatingdevices are added to the biometric imaging device 50. If for example thebiological surface to be imaged is a fingertip which dryness and/ortemperature are lower than an average body temperature and dryness, thecompensating devices adjust the conditions of the fingertip to complywith pre-defined standard conditions. Further, the compensating devices57 and 58 are connected to the processor 53. Therefore, according to thesensed information received from the sensor 54, the processor 53automatically compensates for non-biometric parameters by increasing thefingertip temperature via the thermal unit 58, if the sensor 54 detectsa temperature too low for allowing a non-distorted image of thefingerprint.

Alternatively, the sensors 44 and 54 are omitted from the aboveembodiments of the biometric imaging devices 40 and 50, wherein onlycleaning or other preparation of the fingertip is performed prior toimaging thereof.

Referring to FIGS. 6 and 7, two exemplary images of a fingertip areshown, sensed according to dry and moist conditions of the fingertip. Animage of the fingertip sensed under dry conditions, FIG. 6, exhibitsridge and valley structures, which are broken up into separate segments.For example, the structural elements 61, 62, 63 and 64, 65, 66 mostlikely belong to one continuous feature each. When the environmentalconditions are known when the image is reconstructed, appropriateinterpolation routines are applied as to eliminate possible imagedistortions due to dry environmental conditions. Similarly, an image ofthe fingertip sensed under moist conditions, FIG. 7, exhibits additionalfeatures connecting ridge structures, which blur the image of afingertip. For example, the structural elements 71, 72, 73, 74, 75 and76 are most likely artifacts stemming from adhesive moisture to thefingertip. When the humidity and moisture levels are known when theimage is reconstructed, appropriate data processing routines areemployed to correct for erroneous structural features. Also, when thefingertip is conditioned prior to sensing using the preparation device,it is likely that far less image distortions are recorded when thefingertip is sensed.

The above examples refer to fingerprint imaging using a capacitivecontact swipe imager, but the systems and methods described are equallyapplicable to other contact based biometric imaging including palmscanning and skin imaging in general. Furthermore, the system and methodof the present invention are easily extended to any kind of imageanalysis of a biological feature, which is susceptible to externalconditions.

Although the present invention has been described with respect tospecific embodiments thereof, various changes and modifications areoptionally carried out by those skilled in the art without departingfrom the scope of the invention. Therefore, it is intended that thepresent invention encompass such changes and modifications as fallwithin the scope of the appended claims.

1. A biometric imaging device for imaging a biological feature, thebiometric imaging device comprising: means for sensing the biologicalfeature and for providing sensed image data relating to an image of asurface of the biological feature; means for detecting an effect of asensed environmental parameter on the biological feature, where thesensed environmental parameter is other than a parameter relating tosurface topology of said biological feature; and processing means forcorrecting or restoring the sensed image data in dependence upon thedetected environmental parameter.
 2. A biometric imaging deviceaccording to claim 1, wherein the sensing means comprises a capacitivecontact imaging device, an optical imaging device, or a thermal imagingdevice.
 3. A biometric imaging device according to claim 2, wherein thesensing means comprises a capacitive contact swipe imager that sensesdata in the form of a plurality of partial images, and wherein theprocessing means constructs a composite image from said plurality ofpartial images.
 4. A biometric imaging device according to claim 1,wherein the detecting means comprises a temperature sensor that senses atemperature of the biological surface, and wherein the processing meansimplements data processing algorithms to eliminate artifacts resultingfrom the sensed temperature.
 5. A biometric imaging device according toclaim 1, wherein the detecting means comprises a temperature sensor thatsenses an environmental temperature, and wherein the processing meansimplements data processing algorithms to eliminate artifacts resultingfrom the sensed temperature.
 6. A biometric imaging device according toclaim 1, wherein the detecting means comprises a humidity sensor thatsenses a humidity of the biological surface, and wherein the processingmeans implements data processing algorithms to eliminate artifactscaused by the sensed humidity.
 7. A biometric imaging device accordingto claim 1, wherein the detecting means comprises a humidity sensor thatsenses an environmental humidity, and wherein the processing meansimplements data processing algorithms to eliminate artifacts caused bythe sensed humidity.
 8. A biometric imaging device according to claim 1,wherein the biological feature is a fingertip.
 9. A biometric imagingdevice according to claim 4, wherein the artifacts are discontinuitiesin ridges.
 10. A biometric imaging device according to claim 4, whereinthe artifacts relate to image distortion.
 11. A biometric imaging deviceaccording to claim 5, wherein the artifacts are discontinuities inridges.
 12. A biometric imaging device according to claim 5, wherein theartifacts relate to image distortion.
 13. A biometric imaging deviceaccording to claim 6, wherein the artifacts are discontinuities inridges.
 14. A biometric imaging device according to claim 6, wherein theartifacts are connections between adjacent ridges.
 15. A biometricimaging device according to claim 7, wherein the artifacts arediscontinuities in ridges.
 16. A biometric imaging device according toclaim 7, wherein the artifacts are connections between adjacent ridges.17. A biometric imaging device for imaging a biological feature, thebiometric imaging device comprising: means for sensing the biologicalfeature and for providing sensed image data relating to an image of thebiological feature; preparation means positioned upstream from thesensing means for adjusting an environmental parameter of the biologicalfeature just prior to or simultaneously with a sensing of the biologicalfeature by said sensing means; means for detecting an effect of theenvironmental parameter on the biological feature after adjustment bythe preparation means, where the sensed environmental parameter is otherthan a parameter relating to a surface topology of said biologicalfeature; and processing means for correcting or restoring the sensedimage data in dependence upon the detected environmental parameter. 18.A biometric imaging device according to claim 17, wherein thepreparation means comprises a cleaning station that cleans thebiological feature prior to imaging.
 19. A biometric imaging deviceaccording to claim 18, wherein the cleaning station comprises a handlotion dispenser, an air jet dispenser, a wire brush, or a series of wetand dry sponges.
 20. A biometric imaging device according to claim 17,wherein the preparation means comprises means for adjusting atemperature of the biological information source prior to imaging.
 21. Abiometric imaging device according to claim 17, wherein the preparationmeans comprises means for adjusting a moisture content of the biologicalinformation source prior to imaging.
 22. A biometric imaging device forimaging a biological feature, the biometric imaging device comprising:means for sensing the biological feature and for providing sensed imagedata relating to an image of the biological feature; preparation meanspositioned upstream from the sensing means for adjusting anenvironmental parameter of the biological feature just prior to orsimultaneously with a sensing of the biological feature by said sensingmeans; and means for detecting an effect of the environmental parameteron the biological feature for provision to the preparation means for useby the preparation means in adjusting said environmental parameter ofthe biological feature, where the environmental parameter is other thana parameter relating to a surface topology of said biological feature.23. A biometric imaging device for imaging a biological feature, thebiometric imaging device comprising: means for manipulating anenvironmental parameter of the biological feature; means for sensingimage data of the biological feature downstream from said manipulatingmeans; means for detecting an effect of the environmental parameter onthe biological feature after manipulation by said manipulating means,where the environmental parameter is other than a parameter relating toa surface topology of said biological feature; and means for correctingor restoring the sensed image data in dependence upon the detectedenvironmental parameter.
 24. A biometric imaging device according toclaim 23, wherein the sensed image data is used to determine a type ofmanipulation by said manipulating means.
 25. A biometric imaging deviceaccording to claim 23, wherein the sensed image data is used todetermine an amount of manipulation by said manipulating means.
 26. Abiometric imaging device according to claim 23, wherein the manipulatingmeans includes means for cleaning said biological feature.
 27. Abiometric imaging device comprising: imaging means for sensing afingertip passed there across as for providing sensed image data;cleaning means disposed adjacent the imaging means for cleaning thefingertip as it passes there across, portions of the fingertipcontacting the cleaning means just prior to or simultaneously withpassing across the imaging means, wherein in use portions of thefingertip are cleaned prior to being imaged in order to provide forimaging of a clean fingertip; means for detecting an effect of anenvironmental parameter on the fingertip after cleaning by said cleaningmeans, where the environmental parameter is other than a parameterrelating to a surface topology of said biological feature; and means forcorrecting or restoring the sensed image data in dependence upon thedetected environmental parameter.